Embankment dam and waterproofing method

ABSTRACT

A dam includes a body ( 11 ) made of loose material, for example earth and/or rocks (A), and a water barrier ( 12 ) axially extending to the dam body ( 11 ), including a waterproofing layered membrane ( 13 ) and a zone of waterpermeable loose material (B), on at least one side of the membrane ( 13 ), which can be injected with a sealing fluid and is designed to avoid puncturing of the membrane ( 13 ) and to allow the monitoring of the leakage water due to failures in the waterproofing membrane ( 13 ). The water barrier ( 12 ) can be provided inside the dam body or close to the upstream face.

SCOPE OF INVENTION

This invention refers to embankment dams, and to an improved method fortheir construction and waterproofing.

STATE OF THE ART

Water resources become more and more precious and their conservation isbecoming more and more important; therefore it is essential to searchfor and adopt solutions which minimise the waste of water and whichallow a clever management of the existing water resources.

The most ancient typology of a dam is the embankment dam, obtained byusing natural materials available on site for the creation ofembankments capable of contrasting the pressure exerted by the watercollected in the natural reservoir delimited by the dam itself. The dambody must be statically stable and at the same time it must avoid waterleakage caused by possible infiltration, which would cause a decrease ofthe quantity of water resource available, and which could alsojeopardise the stability or the safety factor of the dam itself. As amatter of fact, uncontrolled water infiltration into the dam body cancause undesirable interstitial pressures, erosion phenomena and theformation of preferential flows or of “piping” capable of causing eventhe collapse of the whole structure.

In many cases earthfill and/or rockfill dams are preferred toconventional concrete dams, to roller compacted concrete (RCC) dams, tomasonry dams or other, as they are less expensive; therefore it isimportant to build embankment dams which have a high safety factor andare watertight.

During the years different techniques have been developed to makeembankment dams watertight. There are substantially two tendencies forthe waterproofing of embankment dams: the first one consists inwaterproofing the upstream face, and the second one consists in creatinga waterproofing core inside the body of the dam itself.

The waterproofing of the upstream face stops possible infiltration ontothe dam surface next to the water impounded in the reservoir. Thewaterproofing barrier is executed on the slopes of the dam body and istherefore subject to stresses and deformations which occur over time inthe dam body. This kind of barrier must therefore have goodcharacteristics of elasticity and at the same time or watertightness.

In general this kind of barrier consists of an upstream face built inconcrete, with waterproofing joints, waterstops In synthetic materialand/or copper, or with facings made of a bituminous concrete.

In both cases the deformations which the dam body undergoes duringexploitation are such as to cause possible failures in thesewaterproofing barriers with subsequent water loss and risk for thestability of the structure.

Recently, watertight upstream facings have been executed with flexiblesynthetic geomembranes, capable of granting the watertightness of thedam and at the same time capable of sustaining strong deformations, evenconcentrated, without damage.

Geomembranes simply laid over the upstream face of the dam, however,need ballasting layers in order to avoid that the geomembrane itself canbe displaced or damaged by the suction exerted by winds, or by thefatigue caused by the action of waves.

A second solution which has been widely adopted in construction ofembankment dam foresees the construction of a central watertight care,made with natural materials positioned so as to grant low permeability,lower than 1×10⁻¹⁰ cm/sec, for example clay or bentonite, placed duringconstruction of the embankment. In the latest decades, the central corehas also been constructed in bituminous concrete and in conglomeratescement-bentonite based.

All the above-mentioned solutions have emphasised some constructivedifficulties, as well as a rather high probability not to be able toreach the required reliability, besides the impossibility of checkingthe extent of their efficiency by measuring the occurring seepage.Furthermore, should infiltration or water leakage through the centralcore occur, the repair is extremely difficult and brings uncertainresults.

An embankment dam of the type mentioned above is described inDE-A-4.402.862; this document suggests also the use of a waterlightening core in bituminous concrete, and a sealing membrane toprovide a small cavity upstream the central core and a filteringmaterial, to allow said cavity to be filled with water upon constructionof the dam, to subject the same dam to the maximum hydrostatic conditionin absence of water into the basin

Type and nature of the membrane is not described or suggested in thisdocument, because the waterproofing of the dam is performed by thebituminous concrete core. Furthermore DE-A-4.402.862 does not suggest ormake obvious to gradually construct the membrane and a transition zoneof loose material, during construction of the dam, as well the use of afine loose material suitable to inject a sealing substance upon failureof the membrane.

Hence, for the construction of embankment dams, the need of finding newconstruction and waterproofing solutions which, by using artificialmaterials, allow to obtain an effective watertightness for the wholelife of the dam, by using systems and materials which can be coupledwith aggregates of the dam body capable of granting only the staticfunction, and which are also easily and economically constructed, whoseefficiency can be checked over time and which, in case of damage, can besimply and efficiently repaired.

OBJECTS OF THE INVENTION

The main object of this invention is to execute an embankment dam and aconstruction and waterproofing method, which can reach theabove-mentioned objectives, allowing to make consistent savings on thetotal cost of construction of the dam.

In particular, an object of this invention is to supply a method for theconstruction and the waterproofing of an embankment dam which uses awatertight barrier capable of adapting to any deformation of the dambody without loosing its efficiency or its watertightness.

A further object of this invention is to supply an embankment dam andconstruction and waterproofing method which allow to adopt suitablemonitoring systems of the watertightness of the waterproofing barrier,and which at the same time allow to intervene for the necessary repairs,or to execute waterproofing connections with other rigid structures ofthe dam itself.

Another object of this invention is to supply a method for theconstruction and the waterproofing of an embankment dam which allows touse an upstream waterproofing system comprising a proper flexiblesynthetic geomembrane extending from the crest to the upstream toe ofthe dam, allowing a non-rigid connection of the geomembrane itself,capable of following the deformations, sometimes high, of the dam bodyitself which can occur over time.

A further object of this invention is to supply a method for theconstruction and the waterproofing of an embankment dam which allows toimmediately use the dam, even if not yet finished, during itsconstruction.

BRIEF DESCRIPTION OF THE INVENTION

According to this invention, a method has been provided for thewaterproofing of a dam comprising an embankment body in coarse loosematerial having a longitudinal axis, in which the aforementioned dambody is made by superimposing layers of earth and/or rocks, and a waterproofing barrier comprising a waterproofing membrane and a transitionzone of fine loose material which develop from the bottom towards thetop and which extend along the longitudinal axis of the dam,characterised by performing the waterproofing barrier including at leastone synthetic and elastically yeildable waterproofing geomembrane anddisposing at least on transition zone of selected loose material on atleast the downstream side of the geomembrane, said loose material havinga high water permeability for the injection, of fluid or fluidisedsealing materials, gradually performing the transition zone and thewaterproofing membrane during the construction of the body of the dambody; and providing anchoring means for progressively anchoring thewaterproofing geomembrane to the transition zone during the constructionof the dam.

According to a first particular aspect of the invention a method hasbeen provided for the construction and the waterproofing of darns forretaining water in a reservoir, in which the dam comprises a body incoarse loose material, made by superimposed layers in earth and/or rockor similar, to provide a static function to resist to the thrustimpounded by the water in the reservoir, the method comprising the stepsof performing a central core defining a water-barrier in selected fineloose material, from sand to gravel, with a high permeability, higherthan the dam body, for instance comprised between 1×10⁻¹ and 1×10⁻⁵cm/sec; this barrier incorporates at least a waterproofing membrane inan elastically yieldable synthetic material, extending from the dam bodyfoundation to the crest, and longitudinally to the dam itself. At leastone side of the waterproofing membrane is covered by at least one layerof synthetic material, for example a geotextile, capable of protectingthe membrane against the mechanical aggression of the inert loosematerials of the central core; the waterproofing membrane and theprotecting layer in synthetic material being progressively incorporatedin the different superimposed layers in loose material, during theconstruction of the dam body and of the central core.

According to another aspect of the invention, a method has been providedfor the construction and the waterproofing of dams designed forretaining water in a reservoir, in which the dam comprises a body incoarse loose material, made of superimposed and compacted layers inearth and/or rock or similar, and a waterproofing membrane in anelastically yieldable synthetic material, extending from the dam bodyfoundation to the crest, and longitudinally on an upstream face of thedam, the waterproofing membrane being fastened by means of strips ofsaid elastically yieldable synthetic material, previously embeddedbetween superimposed layers of loose material of said body of the dam,and successively welded to the waterproofing membrane during theconstruction and the installation on the above-mentioned upstream face.

According to a particular aspect of the invention, the waterproofingmembrane is built on the upstream face of the dam already completed, byadjoining several sheets in synthetic material which are unrolled fromthe top to the bottom of the dam and welded to the anchoring stripsembedded in the dam body during its construction.

According to another particular aspect of the invention, thewaterproofing membrane is built on the upstream face of the dam byadjoining several sheets in synthetic material which are laidhorizontally in respect to the longitudinal axis of the dam and weldedto anchoring strips in synthetic material embedded in the dam bodyduring the construction of the dam itself. This solution is particularlyadvantageous if compared to the previous ones because it allows ananticipate, although partial use of the dam, during its construction,without having to wait for the long time normally required for thestabilsation and testing of the dam after completion.

In the solution with the waterproofing membrane laid directly on theupstream face of the dam, the use of a waterproofing synthetic material,flexible and elastically extensible, coupled and adherent to a substratein if synthetic material, such as a geotextile or similar, besidessupplying a mechanical protection against any accidental puncturing ofthe waterproofing membrane by the loose material of the dam, suppliesalso surface with a high friction coefficient. This surface with highfriction coefficient allows to maintain in their position the singlesheets of the membrane during their installation, even if they are notyet welded to the anchoring strips.

The connection between the anchoring strips and the waterproofingmembrane can be executed by thermo-welding in accordance with specificmethods further explained, by using in any case for the waterproofingmembrane and for the anchoring strips, synthetic materials that arechemically compatible for their heat-welding.

According to one more aspect of the invention, the lower edge of thewaterproofing membrane is fastened to the dam body's upstream toe bycreating a longitudinal bend which allows the membrane itself to betteradapt to possible movements of the dam body.

For the scope of this invention the various words used have the meaningherein defined:

geomembrane: flexible synthetic material with two prevailing dimensions,characterised by a low permeability to fluids;

geocomposite: flexible synthetic material with two prevailingdimensions, made by coupling, during production, of two or more layersof synthetic materials with different characteristics and functions, oneof which consists of a geomembrane having a waterproofing function;

geosynthetic: synthetic material with two prevailing dimensions; whichdepending on its characteristic can have different functions such aswaterproofing, antipuncturing protection, sliding, etc.;

geotextile: synthetic material consisting of textile fibres, with highpermeability;

layered membrane: consists of at least two layers of synthetic materialswith two prevailing dimensions, having different functions, which can becoupled during manufacturing or can be only superimposed during theconstruction of the dam.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further characteristics and advantages of the method forconstruction of embankment dams, as well as of the waterproofing system,will better result from the following description of some examples ofpreferential embodiments.

In the drawings:

FIG. 1 is a front view of a generic dam, part of which has been realisedin loose material according to a first type of realisation of anembankment dam having a central waterproofing core according to thisinvention;

FIG. 2 is a section according to line 2—2 of FIG. 1;

FIG. 3 is a section according to line 3—3 of FIG. 2;

FIG. 4 is an enlarged detail of FIG. 3;

FIG. 5 is an enlarged detail of FIG. 2;

FIG. 6 is an enlarged detail of a second type of an embankment damhaving a central waterproofing core;

FIG. 7 is a cross-sectional view according to line 7—7 of FIG. 6;

FIG. 8 is a schematic view of a scaffolding which can be used for theconstruction of an embankment dam according to the example of FIG. 6;

FIGS. 9 and 10 show some significant constructional phases of anembankment dam having a central core with a double waterproofing layeredmembrane, according to the example of FIG. 6;

FIGS. from 11 to 14 show some significant constructional phases of anembankment dam with a central core having a double layered membraneaccording to an alternative embodiment of the invention.

FIG. 15 shows a first way of constructing a waterproofing barrieraccording to the invention in correspondence of the upstream face;

FIG. 16 shows part of a front view of the waterproofing layered membraneon the upstream face of the dam of FIG. 15;

FIG. 17 shows an enlarged detail of FIG. 15;

FIG. 18 shows a second way of constructing a waterproofing barrier nextto the upstream face;

FIG. 19 shows an enlarged details of FIG. 18;

FIG. 20 shows part of a front view of the waterproofing layered membraneon the upstream face of the dam of the previous figures;

FIG. 21 shows an enlarged detail of an anchoring system at the loweredge of the waterproofing layered membrane;

FIG. 22 is an enlarged detail of FIG. 21.

DETAILED DESCRIPTION OF THE INVENTION

Central Waterproofing Layered Membrane

With reference to FIGS. from 1 to 5 we will describe at first theconceptual scheme and the general construction principles of anembankment dam with a central waterproofing layered membrane, accordingto the invention.

FIG. 1 show an example of a generic dam which includes a part 10 forinstance in concrete, consisting instance in a spillway, an intake toweror other, and a part 11 in coarse loose material, comprises an upstreamdam body 11A and a downstream dam body 11′A in earth and/or rock, and awater-barrier including a central core 12 in fine loose materialsuitably selected to constitute a proper transition layer, havingcharacteristics of permeability and injectability which will be furtherexplained; the core 12 in the example under consideration has been madewaterproof by means of a layered membrane 13 consisting of a “package”of geosynthetics, which extends in the direction of the longitudinalaxis of the dam, starting from a concrete beam 16 for the anchorage tothe foundation of the dam body 11, towards the top, up to the crest, thelayered membrane thus being incorporated in the mass of loose materialwhich forms the central core 12.

In particular, as shown in the detail of FIG. 4, the waterproofingpackage 13 is substantially composed of a geomembrane 14 in synthetic,waterproofing, flexible and elastically yieldable material, for examplein PVC or PE or PP of adequate thickness, and of two lateral protectivesubstrates 15, one on each side, in synthetic material, for example ageotextile, in order to avoid any accidental puncturing of thewaterproofing geomembrane and hence a loss of watertightness of themembrane 13 itself.

As shown in the above-mentioned figures, according to this firstembodiment of the invention, a central core of the waterproofing barrieris constructed, placed vertically or inclined, in fine or granular loosematerial B, adequately selected, preferably monogranular, incorporatinga waterproofing package 13 in synthetic material. This material hasadequate flexibility and elasticity characteristics, to follow and/orcompensate movements of the dam body 11A, 11′A which may occur overtime, without failure; package 13 at the dam upstream toe is fastened toa concrete beam 16 or otherwise connected to the foundation.

Therefore, as shown in the sectional view of FIG. 3, the waterproofingpackage 13 is disposed inside or between two side by side arranged andvertically extending zones constituting the central core 12; these twozones are covered with the different layers A of coarse loose materialcomposing the dam body, placed both on the upstream side and thedownstream side of the artificial waterproofing barrier thusconstructed.

According to the scheme of the above-mentioned figures, package 13 hasthe primary function of waterproofing and watertightness, while theloose material B of core 12 has a transition and, if necessary, adrainage function. On the contrary, the natural or inert material Aconstituting the body 11A and 11′A of the dam, has the sole staticfunction of resisting to the thrust impounded by the water in theupstream reservoir.

During construction as well as during operation of the dam, the centralwaterproofing layer 14 of package 13 is therefore protected on bothsides, the upstream side and the downstream side, by one or moresubstrates 15 of flexible synthetic material, such as geotextile orsimilar. The aim is to favour the distribution of the hydrostaticpressures which act on the dam body itself and which are transmitted tocore 12 as well, as well as to reduce the effect of the mechanicalaggression, by puncturing and/or abrasion, exerted by inert materials onthe geomembrane of the water barrier, as previously discussed.

Layer 15 of protection synthetic material can be independent frominternal layer 14 (geomembrane) or can be hot-coupled to it like asandwich. The waterproofing layered membrane consisting of layer 14 andof protecting geotextiles 15 is therefore in contact with a layer ofadequately selected fine loose material, for instance granular material,such as sand, stony material such as gravel or similar, with dimensionsranging between 3 mm and 30 mm approximately. The dimensions of theloose material can be greater and even reach 10 cm, according to therequirements for transition and drainage of the central core; even if itis not necessary, it is generally preferred that material B of thetransition area of core 12 is a monogranular material or, e.g., it maybe requested that the selected material which forms the downstream zoneof the central core has a high degree of permeability to fluids,comprised approx. between about 1×10⁻¹ and 1×10⁻⁵ cm/sec in order toallow, if needed, efficient drainage of the water which could seepthrough cracks or local failure of geomembrane 14.

Therefore the combination of the selected material B of core 12, ofgeotextiles 15 and geomembrane 14 allows to create an effectivewaterproofing and at the same time an optimal transfer of the staticloads from body 11A to body 11′A of the dam, through core 12, while atthe same time constructing an effective coupling of the variousseparation interfaces between material A which forms body 11A, 11′A ofthe dam, generally consisting of earth and/or rock, and the selectedstony material B constituting central core 12.

As previously mentioned, at the dam bottom along the entire foundationline, package 13 is watertightly and intimately connected to a concretebeam 16, or a similar anchoring mean, from which a waterproofing screen16′ departs towards the underlying soil; this waterproofing screen isexecuted for example by means of grouting with concrete or resins orsimilar and more generally by plastic diaphragms.

The perimeter beam 16 can be independent or be part of an inspectiongallery (not shown) placed at the dam base, in axis with central care12.

The fundamental reason for the presence of the foundation beam or ofother equivalent structure is to have an anchoring element for thegeomembrane, and a connection between the waterproofing barriers overand under the foundation plan.

Behind package 13, on the downstream side, starting from layer B in fineselected material of central core 12, at the bottom of central core 12,in correspondence of beam 16, it is possible to create a drainage pipesystem. The system consists of pipes 17 which are inclined towards thedam's downstream side and are able to collect any water infiltrationthrough cracks or failure of package 13 which can consequently bemonitored.

The drained waters can be conveyed to one or more collecting points 17′where they are monitored by means of proper devices and successivelydischarged downstream.

The above-mentioned system provides the following advantages:

1) It creates a continuous artificial waterproofing barrier, in flexiblesynthetic material, which extends from the foundation to the crest ofthe dam body. The waterproofing barrier can continue to reach the deeplayers of the ground by means of screen 16′, executed by grouting orwith suitable plastic diaphragms, which departs from the foundation beam16 which thus constitutes the connecting element;

2) It constructs a watertight core, able to follow the dam body'sdeformations which occur over time due to the settlement which the dambody itself undergoes due to its own weight and to the hydrostatic load,keeping the waterproofing and deformability characteristics of thewaterproofing core unaltered over time;

3) it verifies the efficiency of the waterproofing system by means ofthe monitoring system placed downstream of the central core itself.

Connection with Rigid Structures

In some situations, as schematically represented in FIG. 1, it may occurthat body 11A, 11′A of the embankment dam, with waterproofing core 12and package 13, are in contact with rigid parts of the dam itself, forexample executed in conventional concrete, in roller compacted concrete(RCC), in masonry or other.

This situation occurs when only a part of the dam is built in loosematerial, while the other part is a gravity dam executed withconventional techniques. The same situation occurs also when an intaketower, executed in concrete or masonry, is inserted in the body of theembankment dam.

In these cases, it is necessary to achieve the continuity of thewaterproofing between package 13 of the central core of the embankmentdam, subject to greater deformations, and the part of structure 10, morerigid, subject to smaller deformations.

For this purpose, as schematically shown in FIG. 5, the connection ofthe waterproofing package 13 to the rigid body 10 of the dam can be madeby means of one or more strips 18 consisting of bands 18′ ofsupplementary layered membranes, of the same material as package 13,installed vertically like in a bellows-shape, adherent to the rigid body10 as shown. A vertical edge of the bellows-shaped package 18 iswatertight anchored to the rigid body of the dam by means of mechanicalfastening devices, schematically shown, e.g. by means of metal profileswhich fasten by compression the edge of strip 18 folded in abellows-shape against the rigid body 10, to which the profiles arefastened by means of bolts and washers 20, while the other vertical edgeof strip 18 is heat-welded to the correspondent opposite edge of package13. Strip 18 will thus form a kind of bellows-shaped folds, like in abellows. The folds are executed by welding geomembrane bands 18′according to the “joined-hands” scheme, or by folding a membrane stripon itself. This bellows-shaped folded element which faces the dam body11A, 11′A in loose material, is left free to move or to follow thedeformations which the dam can be subjected to over time.

The connection between package 13 of the central core and the striplayered, bellows-shaped membrane 18, can be executed directly or bymeans of supplementary elastic strips suitably shaped with extramaterial, and made of the same material as package 13.

The bellows can be protected on its sides by further elastic strips.Strips 18′ of the bellows, made of the same material as package 13, areproperly shaped or welded in the “joined-hands” configuration, withextra material, so that they can form further supplementary deformablebellows.

Between the bellows' strips made of layered membrane, and above them,other layers of material 19 can be placed, which reduce the friction andtherefore facilitate the relative sliding (geotextile, synthetic liners,layers of silicon, of Teflon, sand, etc.), and which supply a furtherprotection to the bellows.

The settlement of dam body 11A, 11′A in loose material will thereforeproduce stresses in the contact surface between body 11A, 11′A and therigid body 10; in this zone the bellows-shaped layered membrane isinstalled, which, due to its geometric shape and to the elasticcharacteristics of the material with which it has been made, will allowto follow this settlement.

Practically body 11A, 11′A in loose material settles, causing acorrespondent lowering of the elevations of the different layers of thepackage of the layered membrane 13 contained in the central core 12.Since package 13 is connected to the external edge of the strip of thebellows-shaped layered membrane 18, also this one will be compelled togo down according to the settlement of body 11A, 11′A of the dam. Theinternal edge of the bellows-shaped membrane 18 is on the contraryrigidly connected to the rigid part 10 of the dam, as previouslydescribed. Therefore, the variation in position between the internaledge which remains fixed, and the external edge which goes down, will beabsorbed partly by the folds of bellows 18, partly by the supplementaryconnection strips, if present, as well as by the minimum rotation of thebands of the bellows itself and by the elasticity of the material whichpackage 13 is made of.

The described solution is such that, while the fill constituting body11A and 11′A of the embankment dam settles, package 13 can freely followsuch settlements while keeping the waterproofing connection with therigid structure 10.

In certain situations it would even be possible to avoid the use of thebellows-shaped membrane 18, as the settlement of body 11A, 11′A in loosematerial normally occurs in an almost homogeneous and linear way;therefore, the supplementary elastic strips alone could provide a highsafety coefficient by coping with the induced deformation and theresulting stress, since package 13 and the bellows strips 18, which areable to undergo elongation at break which can reach 200% and more,contribute to absorb the deformations and the stresses.

Central Double Waterproofing Membrane

FIGS. 1-5 show the use of a single package 13 as a waterproofing elementof the central core 12; other solutions are nevertheless possible, oneof which is shown in FIGS. 6 and 7 of the attached drawings.

As shown in these figures, in order to increase the safety andwaterproofing degree of the central core 12, it is possible to installtwo adjoining packages 131 and 132 in impermeable synthetic andelastically yieldable material, perfectly identical to package 13. Thetwo packages are at a suitable distance one from the other, and arepositioned parallel to the longitudinal axis of the dam, from the baseof the body in loose material 11A, 11′A, to the crest of the dam.

In this case, the central core 12 in selected loose material includes anintermediate zone 121 placed in the gap between the two packages 131 and132, and two lateral confinement zones 122, 123.

The intermediate zone 121 thus created must have a grading suitable toallow the injection, if necessary, of fluid or fluidised substances forthe sealing of leakage, such as bentonite sludge or other, capable oflocally creating or restoring watertightness in case of puncturing orfailure of package 131.

Also in this case, both packages 131 and 132 are placed inside a fine orgranular material selected, from sand to gravely, as previously shown,and are protected on both faces by a Layer of flexible syntheticmaterial 15, of geotextile type, with an anti-puncturing and anti-gripfunction.

The selected material of the zone 121 between the two packages 131, 132must allow an adequate transfer of the loads from one side of the dambody to the other one and must always have a high degree ofinjectability for the foreseen scopes, creating a homogeneous staticbody.

Also in this case the two packages 131 and 132 are fastened to the damperimeter, on the foundation, with a watertight mechanical anchorage.Again, from the concrete perimeter beam 16 or similar can depart awaterproofing screen 16′ executed by grouting or by plastic diaphragms,as previously mentioned.

In general, the fine selected material of zone 121 placed between thetwo membranes, and if necessary the fine selected material of the twolateral zones 122 and 123, can be of the same type B previouslydescribed for the central core 12 of the example or FIG. 1, namely itmust have a high decree or injectability and draining capacity; yet,according to the requirements, it is possible to use selected materialsB and C with different draining characteristics for the three zones 121,122 and 123 of the central core, as shown in FIG. 6.

The example of FIG. 7 shows another variant which is possible if theconfiguration with the two packages 131 and 132 is adopted.

As shown in FIG. 7, the two packages, the upstream one 131 and thedownstream one 132, can be connected one with the other, at prefixeddistances, with transversal connections made 23 with other strips of thesame package, in order to create separate blocks in the intermediatezone 121 of the central core. The blocks can be monitored and drainedindividually, thus allowing to detect with greater accuracy any leakageor inefficiency of the waterproofing system.

The above-mentioned double-package system allows the followingadvantages:

1) it creates a continuous artificial double waterproofing barrier, inflexible synthetic material, which again extends from the foundation upto the crest. The waterproofing barrier thus created can be extended toreach the deep layers of the ground by means of a screen obtained bygrouting with suitable material, or by a plastic diaphragm, based onconcrete-bentonite mixtures, starting from the foundation beam 16.Moreover, the upstream barrier consisting of the first waterproofingpackage 131 grants the required watertightness, while the secondwaterproofing package 132, downstream constitutes a safety barrier;

2) it creates a waterproofing barrier capable of following thedeformations of the dam body which occur over time and due to thehydrostatic load, maintaining the waterproofing and deformabilitycharacteristics unaltered;

3) it allows to test the efficiency of the waterproofing system by meansof the monitoring system placed downstream of both packages, by means ofa pipe system 17 which collects any infiltration or leakage downstreamof the second package 132, as well as by means of a second system ofpipes 22 which open towards he gap delimited by the two packages 131 and132, in order to collect the infiltration or the leakage coming from theupstream package 131, through the layer of draining material 121 of thecentral core;

4) in case of deficiencies of the upstream package 131 it is possible toexecute waterproofing grouting of zone 121 with conventional techniquessuch as grouting with bentonite or other suitable material, eitherlocally or, in the entire zone 121 of selected material placed in thegap between the two packages. Therefore the two packages 131 and 132shall carry out, besides the waterproofing function, also a confinementfunction for the future grouting of waterproofing material, thusallowing to restore the watertightness of the water barrier. The wholesystem is very simple and efficient, since the high degree ofinjectability of the layer of material of the intermediate zone 121allows to insert suitable grouting pipes, until the desired point isreached; however it is better to position the injection pipes atprefixed locations, during the construction phases of core 12. Moreover,the system of draining pipe 17 and/or 22 allows to verify the efficiencyof the repair intervention carried out as described.

As an alternative to this embodiment, it is possible to extend package13 of FIG. 3 or package 131 of FIG. 6 towards the upstream toe of thedam body in order to build the foundation beam 16 in correspondence ofthe upstream toe itself, at connection with the upstream face.

This alternative solution would allow in some cases to reduce the depthof screen 16′ with evident economical advantages; furthermore, thesolution gives the possibility of further intervening on the samescreen, even after completion of the dam and after dewatering thereservoir, since beam 16 would be in an accessible position, instead ofbeing confined under the central core. It is also possible to furtherextend package 13 or 131 upstream, inside the reservoir created by thedam, by eliminating in this case the construction of the perimeter beam16 on the upstream toe.

A further constructional alternative of the central core and of thewaterproofing geomembranes is shown by the examples of FIGS. from 11 to14. In particular, with reference to FIG. 14, in this case the twopackages 131 and 132 are executed by a plurality of inclined stripshaving the tipical disposition, of a “Christmas tree”, that is to saywith the strips of each package placed inclined alternatively inopposite directions, suitably heat-welded along their longitudinaledges.

More precisely, both packages 131 and 132 have been executed by means ofa plurality of heat-welded strips 25.1-25.n and 26.1-26.n, alternativelyinclined upstream and downstream with the natural friction angle of theloose material used (normally between 15° and 40° in respect to ahorizontal plan) according to the characteristics of the materialsemployed, and to the thickness of the layers of loose material A and Bwhich constitute body 11A, 11′A of the dam and the various sections 121,122 and 123 of selected ill, constituting the central core, or infunction of other circumstances or necessities.

Also in this case the characteristics of the loose material used for thevarious layers of the various sections of the central core can be thesame or different, depending on the specific requirements.

Various constructive techniques are possible depending or the type andcharacteristics of the geomembranes employed, that is to say if thegeomembrane or the geomembranes result from joining of vertical strips,or from joining of inclined strips.

Constructive Methods

In general, the packages are installed following the constructionalphases of the “embankment”; therefore the upper elevation of the centralcore 12 increases with the elevation of the body 11A, 11′A of the dam.Furthermore, the choice of the typology depends on whether it isnecessary to connect with a rigid body 10, which is not always present.

In general, according to the examples of the various figures, the firstoperation to be performed is the execution of the foundation beam 16which may or may not be a part of a possible perimeter inspectiongallery. Then the packages are connected to the perimeter beam withmechanical fastenings or other type of anchorage which can grantwatertightness in presence of hydraulic loads not inferior to theservice ones.

In the various hypothesised cases the intermediate zone of the centralcore, comprised between the two packages will be put in contact with themonitoring and drainage discharge system. Then the construction of thedam body and the central core will begin, for example according to oneof the two methods described here below.

Construction by vertical sectors can be executed by means of extractableformworks, according to the example of FIGS. 6 and 8 and the phasesshown in FIGS. 9 and 10 of the drawings attached.

In particular FIG. 8 shows a possible type of realisation of extractableformworks 27, substantially consisting of two lateral walls 28, 29parallelly placed and kept apart by means of upper crosspieces 30 andcriss-crossed bars 31. Number 32 indicates two hooking structures forhoisting formworks 27 by means of arm 33 of a crane, or by means of anyother suitable hoisting device. The distance between the two lateralwalls 28, 29 of the formworks substantially corresponds to the width ofthe intermediate area 121 of the central core, included between the twopackages 131 and 132.

The fundamental construction phases which characterise this first methodare illustrated in FIGS. 9 and 10 which represent intermediate momentsin the construction of the central core and of the dam body.

According to this first constructional technique, the elements offormworks 27 are placed side by side, aligned with the longitudinal axisof the dam, till they cover the whole length of the section interested.In these conditions the geomembrane strips contained in packages 131 and132 are placed on both sides of the formworks and laterally foldedtowards the outside. The geomembranes are then laid on formworks 27 withthe interposition of a geotextile layer on both sides. The upper part ofthe two geomembrane strips with the geotextiles are fastened at topswith temporary anchors, for example with clamps or other. Thegeomembranes, supplied in rolls, are heat-joined one to the other inorder to get a total length equivalent to the total length of thevarious elements of the formworks which are positioned along thelongitudinal axis of the dam body to be executed. If needed, it ispossible to create transverse compartmentation sectors 23 of theintermediate area of the central core, by transversally interposingbetween contiguous formworks, between the abutting faces, othergeomembrane strips, protected by geotextiles, which are heat-coupled onthe two edges to the upstream and downstream geomembrane stripspositioned horizontally on the two sides of the central core.

The construction of the embankment can then start or continue. The firstoperation is the spreading and compacting by layers of the selectedmaterial of the central core 122 and 123, placed upstream and downstreamof the formworks, and of the material of zone 121 placed inside theformworks in contact with the geotextile placed as a protection of thegeomembrane on both faces.

Then the material with the biggest dimensions which constitutes body11A, 11′A of the dam, upstream and downstream of the central core islaid and compacted. These operations continue until the dam body reachesan elevation close to the upper edge of the formworks which thereforeresult in the end embedded in the dam body.

The clamps which fasten the geomembranes and the geotextiles areremoved, and the geomembranes with the geotextiles are folded again onthe sides of formworks 27, as shown in FIG. 9. By means of a crane orother suitable hoisting device formworks 27 are removed for almost theirwhole height, if necessary, also by applying to it some vibrators whichcan favour the operation and contribute to compacting the material ofthe core. The formworks are then positioned for the execution of furtherlayers of core 12 consisting of 121, 122 and 123, and of body 11A, 11′Aof the dam. New geomembrane rolls are laid on the embankment, theiredges overlapping on the ones of the geomembrane strips which havealready been embedded in the central core under construction. Theconnection welds are executed, and their watertightness is tested. Thenew geomembrane strips are then uplifted and fastened again overformworks 27, as shown with dashed lines in FIG. 10, always previouslyinterposing the geotextile layers. The installation and compaction ofthe selected material of the central core 12 and of the other inertmaterials of the dam body 11A, 11′A starts again according to the phasespreviously described, till the final elevation of the crest of the dambody is reached.

At last, a continuous concrete slab is built on the crest, and the upperedges o the two geomembrane 131 and 132, which have been thus executedand incorporated in the selected and injectable loose material of thecentral core, are mechanically fastened to it.

As an alternative to the above-described solution, which uses aplurality of formworks open along all the peripheral edges, the varioushorizontal strips of the geomembrane can be vertically fastened to aplurality of fixed or removable linear supports. The supports canconsist of rigid pipes in plastic material, which can be used also forany future injections or be of other type. The construction of thecentral core and of the dam body occurs substantially according to thesame method adopted with the extractable formworks. The verticalsupports, if removable, can be used again as the elevation of theembankment increases, or can be left as permanent supports, embedded inthe central core itself. If injection pipes are adopted as temporarysupport of the geomembranes, when construction is completed, and shouldinjections be carried out inside the core to waterproof it, the pipesthemselves could be used for this purpose.

The constructional technique with the “zigzagged” or “Christmas tree”geomembranes is shown in the following FIGS. from 11 to 14, whichrepresent some of the fundamental phases of this constructionaltechnique.

The first strips of the two packages 131 and 132 are preliminarlyfastened to the foundation beam 16 by means of proper watertightanchoring devices 34. The geomembranes are again supplied in rolls,joined one to the other in order to obtain a length equivalent to thetotal length of the core at the relevant elevation of the foundation;the two first strips of the geomembranes are folded towards the outsideas in FIG. 11.

It is then possible to start the construction of the embankment; atfirst, a first layer of selected material constituting the intermediatezone 121 of the core, and the two upstream and downstream layers of body11A, 11′A of the dam, are laid down and compacted. Then the twogeomembrane strips are folded inside, along the inclined sides of thelayer of material 121, as described in FIG. 12.

Subsequently, two overlapped layers of selected material are laid andcompacted in the upstream zone 122 and in the downstream zone 123 of thecentral core, as it is schematically shown in FIG. 13.

Then the two following strips 131 and 132 are placed, with aninclination opposite to the previous ones, laying them on the laterallayers 122 and 123, which have been previously laid and compacted, andjoining them with the underlying strips.

The construction of the embankment and of the central core with the two“zigzag” or “Christmas tree” packages continues in the same was insubsequent stages, as shown in FIG. 14, till the final height of theembankment and of the central core, required for the dam body to beexecuted, are reached.

During the construction of the central core and of the two “Christmastree” packages, vertical compartmentation sectors can be created byinterposing, transversally to the longitudinal axis of the core, othergeomembrane strips heat-coupled to the two upstream and downstreamlongitudinal geomembranes under construction. Also in this case thevarious geomembrane strips are protected on both sides with geotextilesas in the previous case.

Again, at the end a final crest is built, consisting of a continuousslab made of concrete or bituminous concrete or another suitablematerial, to which the upper edges of the two packages are mechanicallyfastened.

As mentioned several times, the material used for the waterproofing ofthe core is a geomembrane in synthetic, flexible, elastically yieldingmaterial, with a high thickness, or example with a thickness comprisedbetween 2 mm and 4 mm, capable of resisting the high puncturing andabrasion stresses which can arise in correspondence of the contactinterfaces with the loose material of the central core. The geomembraneis also capable of resisting the deformations—even concentrated—whichthe dam body can undergo over time; therefore, the geomembrane must bemade of a thermoplastic or elastomeric material able to allow even highelastic elongation. The junctions of the geomembrane strips can beexecuted with any suitable technique, for example by hot-air welding,keeping the possibility of carrying out tests of the efficiency of thewelds themselves.

The geotextile adopted for the protection of the geomembranes shall havea sufficient mass to grant a high resistance to puncturing and gooddraining characteristics. Should the project specifications require it,both for the construction method with formworks and for the “Christmastree” construction method, the geomembrane could be heat-coupled to thegeotextile during extrusion in order to improve the characteristics ofmechanical resistance of the waterproofing package thus constructed.

From what said and shown it is therefore clear that we have supplied anembankment dam with a waterproofing central core, and a method forconstructing and waterproofing it by means of a single layered membraneor a double layered membrane, which do not require onerous operationsand complex job-site equipment. The construction of the waterproofingcentral core occurs at the same time as the construction of the earthand/or rock embankment of the dam body.

The proposed solutions can be executed with synthetic materials havingperformances exceeding the results of the theoretic calculations;moreover, the production and the preparation of the waterproofingsynthetic material occurs in the factory, under controlled conditionswhich grant constant quality.

The downstream zone of the central core, situated immediately downstreamthe geomembranes, consists of selected material of high permeability,through which it is possible to detect any water seepage, and whichallows a continuous monitoring of the efficiency of the waterproofingsystem. The material which the central core is made of can befurthermore injected with sealing fluids so that it allows the creationof a new waterproofing barrier if needed, in localised areas or alongthe entire length and height of the central core.

The described solutions guarantee very long durability. The use ofgeomembranes for waterproofing of the central core guarantees highreliability since geomembranes of this type have been operating for agreat number of years on the facing of conventional dams. Acceleratedageing tests, carried out in the laboratory, have hypothesised aduration of the waterproofing material exceeding 500 years. Furthermore,the geomembranes themselves, by being embedded in the central core, areprotected from the action of the ultraviolet rays and from vandalism,and are therefore practically indestructible.

Waterproofing Layered Membrane on the Upstream Face

With reference to the FIGS. from 15 to 17, we will now describe avariant of the invention which allows the construction and waterproofingof embankment dams; including an exposed barrier on the upstream side,where a layered waterproofing membrane is laid and suitably anchored tothe surface of the dam upstream face, so as to allow the layeredmembrane to follow and/or adapt to any settlement movements of the damthus constructed.

Also in case of FIGS. 15-17, the dam body 211 is executed with asuitable loose material, earth and/or rock, suitably placed by layers212.1-212.n, superimposed and compacted.

In this case on the surface of the upstream face a waterproofing lineris provided, comprising a waterproofing package 213, whose compositionis similar to the composition of waterproofing packages 13, 131, 132 ofthe previous examples. Therefore the waterproofing package 213 consistsof several adjoining bands or sheets 214, which extend in the directionof the slope of the upstream face, between the crest of the dam and theupstream foundation toe.

The single bands 214 of sheet material are unrolled and laid down on theupstream surface of the dam, and are fastened as they are placed toanchoring strips 215 in flexible synthetic material, suitably embeddedbetween superimposed layers 212.1-212.n of the dam body.

The sheet material of the waterproofing package 213 is preferably ageocomposite including a layer of flexible and waterproofing syntheticmaterial, coupled to a substrate of synthetic material having differentproperties. In particular the superficial layer, which will be incontact with the water impounded in the reservoir of the dam, andtherefore exposed also to the atmosphere, consists of a flexiblesynthetic geomembrane, impermeable and elastically yielding, for examplein PVC, PP, PE or similar, while the underlying layer which will be incontact with the surface of the dam, consists of a geotextile whichperforms the function of protective layer to avoid puncturing of thegeomembrane, and at the same time supplies dimensional stabilityimproving the friction coefficient of the composite geomembrane thusobtained.

Depending on the type of geotextile material adopted, and depending onthe stony material and/or the characteristics of the materialconstituting the surface of the dam with which the geocomposite will bein contact, in general a natural friction angle is created, comprisedbetween 25 and 38 degrees. This means that depending or the slope of theupstream face of the dam, always included between the above-mentioneddegrees, or inferior, during the installation of the waterproofingmembrane the sheets of material 214, before being welded to theanchoring strips 215, remain stable and therefore do not slide,facilitating the installation. The waterproofing package 213 can also bebuilt so that the waterproofing geomembrane is independent from thegeotextile which performs the function of protective layer. In this casethe geotextile sheets are installed in contact with the upstream face ofthe dam, on which they are stable during installation, and thewaterproofing geomembrane is placed over the geotextile and anchored tosheets 215.

As previously described, the single sheets of material 214 which composethe waterproofing package 213 must in any case be anchored to the dambody; should sheets 214 consist of a geocomposite (waterproofinggeomembrane coupled to the geotextile), the underlying layer geotextileco-operates in granting their stability and their resistance to sliding,to resist the actions due to waves and to wind in the part uncovered bywater, and their resistance to loads due to possible sediments oraccidental loads which can affect the geomembrane, or to anyunderpressures which could be generated at the back side of package 213,in case of rapid dewatering of the reservoir.

The anchorage of the single sheets of material 214 which compose thewaterproofing package 213 is made by means of strips 215. For thispurpose, the anchoring strips 215 can be constituted with the samematerial which constitutes package 213, or with a synthetic materialhaving similar chemical characteristics in order to allow welding bythermo-fusion.

In particular, as shown in the example of FIG. 16, and in the detail ofFIG. 17, the anchoring strips 215 are laid between superimposed layersof the loose material constituting the dam body, during construction ofthe dam itself.

The anchoring strips 215 are placed parallel to the longitudinal axis ofthe dam and in such a way that the waterproofing synthetic material,which can be welded, faces the reservoir of the dam. The strips have aback side 215′ which is placed on a substantially horizontal plan,firmly fastened between two superimposed layers 212′ and 212″ of thestony material constituting the dam body. The anchoring strips 215extends outside of the dam body with a front wing 215″ which by gravitylies downwards in an L shape, against the external surface of theupstream face, in correspondence of the lower layer 212′. Inalternative, the same wing 215″ can be folded upwards against the upperlayer 212″ after its construction.

As shown in FIG. 16, the anchoring strips 215 are placed at differentelevations, on several lines, maintaining an alternate or staggereddisposition between the anchoring strips of one line and the anchoringstrips of the two contiguous lines, with interaxis or distances whichcan vary, and at different elevations, depending on each specificproject.

The sheets of waterproofing material 214 rolled up in rolls areprogressively laid starting from the crest, or from any intermediateelevation, towards the dam upstream toe, and during their unrolling theywill progressively cover the anchoring strips 215 which have beenembedded in the layers of loose material which form the dam body.

In correspondence of the overlapping of the sheets constituting package21 with the wings 215″ of the anchoring strips, part of the geotextilelayer is removed or cut-out from each geocomposite sheet 214, creating awelding area 216, so that the back surface of the layer of syntheticmaterial of the geomembrane, in the area 216 uncovered by thegeotextile, is in contact with the front surface of wing 215″, which isin a material chemically compatible, in order to allow the welding bythermo-fusion. In case the waterproofing geomembrane and the geotextileare independent, before the installation of sheets 214 it will benecessary to remove the section of geotextile in correspondence ofstrips 215, in order to create the welding area 216.

Welding can occur by points, by lines or on the whole surface of area215″ of the anchoring wing according to the requirements of eachproject.

As shown in FIG. 17, in a way similar to the previous examples, atransition and draining zone 217 is created between the waterproofingpackage 213 and the earthfill and/or rockfill, during the constructionof the dam. Zone 217 consists of gravel and/or material with a suitablegrading, permeable to water for the drainage of any leakage, andinjectable by sealing fluids.

A second alternative for the fastening of the waterproofing membrane tothe dam body is shown in FIGS. 18 and 19 of the drawings attached.

As shown, also in this case the dam body is formed by superimposedlayers 312′-312″, foreseeing during the construction of the dam theinsertion of anchoring strips 315 to which the waterproofing membrane313, perfectly identical or similar to the one of the previous examples,is then welded.

In case of FIGS. 18 and 19, unlike in the previous example where theanchoring strips 215 were folded in an L shape downwards or upwardsagainst the upstream face of the dam, in this case during theconstruction of the dam body by superimposed layers, the anchoringstrips 315 are “C” folded, so that each anchoring strip 315 has a firstextreme part 315′ embedded in the material of one layer, a secondextreme part 315″ embedded between the material of the previous layerand the material of the following layer, and an intermediate part 315″for welding the waterproofing membrane 313 which extends on the frontsurface of the dam body, between the two extreme parts 315′ and 315″ ofthe same anchoring strip.

Also in this case, if the waterproofing membrane 313 is a geocomposite,the back geotextile layer shall be removed, while if the geotextile isindependent it shall be removed in correspondence with strips 315, inorder to create in any case a welding area 316, also providing betweenmembrane 313 and the earth and/or rock layers of the dam body, atransition and drainage zone 317 in loose material with a fine grading,as in the previous case.

In all cases, in order to obtain a higher protection degree for themembrane, a further protection layer consisting of a geotextile orsimilar can be optionally provided between the membrane and thetransition and/or drainage zone 12, 122, 123, 212 and 312.

In the previous examples, as shown in FIG. 16, a disposition parallel tothe slope of the dam upstream face has been hypothesised for the sheetsof material 214 which constitute the waterproofing membrane; yet, it isevident that the installation of the membrane, instead of by bandsparallel to the slope, can be executed by horizontal bands, asschematically shown in FIG. 20, starting in this case from the damupstream toe and proceeding towards the crest, and partially overlappingthe horizontal edges of contiguous bands; in this way it is possible topartially exploit the dam during its construction. In alternative towhat previously described, the anchoring strips 215 or 315, instead ofcreating distanced anchoring points, could be prolonged for part or forthe whole length of the dam, practically creating continuous weldingareas. Both in case of installation of sheets 214 parallel to the slope,and of installation by horizontal bands, loss of watertightness thatshould occur in the membrane, in damaged areas, can be repaired bywelding elements of synthetic materials identical or compatible with thematerial of the membrane itself.

The advantage of the solutions with geomembrane on the upstream faceconsists in the fact that a continuous waterproofing liner, installed onthe surface of the upstream face, prevents water from infiltrate intothe upstream part of the dam body.

Perimeter Anchorage

In all cases suitable anchoring devices of the waterproofing membraneshall be provided in correspondence of the upstream toe and of the crestof the dam.

At crest, the waterproofing membrane can be, for example, embedded in atrench where the edge of the membrane is laid down and suitablyballasted with gravel or other material, or can be anchored by amechanical, anchorage whenever there is a concrete structure, forexample a road curb, a parapet wall or other structure which normallyconstitutes the upper finishing of the dam.

The fastening of the membrane to the upstream toe of the dam and alongthe whole periphery, in case of FIGS. from 15 to 20 can be executed inany way which is adequate to grant a continuity of the waterproofingbarrier towards the underlying ground, for example as shown in FIG. 15and in the detail of FIG. 21.

In this case the execution of a concrete perimeter plinth 400 isforeseen, to which the lower edge of the waterproofing membrane 213 iswatertight anchored, by folding it forward and against the upper surfaceof plinth 400, if necessary regularised by means or suitable resins, towhich the edge of the membrane itself is fastened by means of a metalprofile 401 which compresses membrane 213 against plinth 400 With theinterposition of a gasket strip 402 and/or of a regularisation layer405; profile 401 is anchored to plinth 400 by means of a plurality ofthreaded rods 403 partially embedded or secured in the concrete of theplinth, on which fastening nuts 404 are screwed. Another way ofanchoring the membrane to plinth 400 can be an “insert” type anchorage:a slot is created in plinth 400 into which the membrane is inserted andthen watertight anchored by embedment in proper waterproofing substancessuch as epoxy resins or similar.

The anchorage of the membrane to plinth 400 also allows to executegrouting of proper fluid substances for the creation of a waterproofingscreen which prevents water from entering between plinth 400 and thecontact surface with the foundation ground, in a way similar to the caseof FIG. 3.

The anchorage to plinth 400 provides a soft connection of the membranebetween the dam body and the base plinth, as illustrated in FIG. 21.

For this purpose, the lower edge of membrane 213 is folded to create abend 220 along a trench 221 executed between the inside edge of plinth400 and the transition zone 217.

The advantage of this solution is that in case settlements occur in thedam body, bend 220 allows the membrane 213 to deform following themovements of the dam body, creating an elongation compatible with themechanical resistance of the membrane itself. If so required, it is alsopossible to create a layer of anti-grip material and provide a layer ofprotective geotextile along the trench for creation of the bend, betweenmembrane 213 and zone 217.

Should the waterproofing membrane be ballasted with a covering element222, as schematically shown in FIG. 21, trench 221 can be filled with alayer of loose material with a very fine grading, for example sand,which does not oppose a substantial resistance to the movement ofmembrane 213 in case it is subjected to tensile stress due to movementand/or settlements of the dam body. The filling layer will be aprotection for membrane 213 from any mechanical action by ballast 222.If needed, it is also possible to create a layer of anti-grip materialand provide a layer of protection geotextile, along the trench forcreation of the bend, between membrane 213 and area 221.

The advantage of using a geocomposite consists in the fact that thegeotextile substrate, if coupled adherent to the PVC waterproofing layeror other proper elastically deformable synthetic material, supplies anincrease in the mechanical resistance of the geocomposite itself.Therefore, in the event that significant deformations are caused in thegeocomposite, normally in the range of 10-20%, the geotextile substratewhich is heat-welded to the PVC layer or similar layer, is detached fromit, allowing the two layers to become independent. Therefore, due to thestrong friction, the geotextile will remain adherent to the diaphragmconsisting of the layer of transition material in the dam body, whilethe elastic PVC geomembrane or similar, having an elongation coefficientwhich is significantly higher and which can reach values as high as300%, will be able to move freely on the underlying geotextile and totherefore contribute with a larger surface to the distribution of thestresses.

However, it is clear that what has been said and shown with reference tothe attached drawings has been given as an exemplification andillustration of the general principles of the invention, and of some ofits preferential configurations, and that it is intended that othermodifications and alternatives are possible both to the structure of thedam, to the structure of the transition core and/or of the waterproofingmembrane, and in the construction techniques, without departing fromwhat as being claimed.

What is claimed is:
 1. A method of waterproofing a dam duringconstruction of the dam, where the dam has a longitudinal axis, anembankment body of superimposed layers of earth and/or rocks, awaterproofing geomembrane, and at least one transition zone of fineloose materials that develop from a bottom to a top of the embankmentbody and along the longitudinal axis of the dam, the method comprisingthe steps of: disposing the transition zone on at least a downstreamside of the geomembrane; partially embedding and securing anchoringstrips into at least one of the transition zone and the embankment body;gradually extending the geomembrane on the transition zone duringconstruction of the dam; and anchoring the geomembrane to the transitionzone by heat-welding the geomembrane to the anchoring strips.
 2. Themethod according to claim 1, further comprising the step of providing asupporting substrate of geotextile synthetic material, coupled to thewaterproofing geomembrane on a side facing towards the transition zone.3. The method according to claim 2, further comprising the step ofproviding an additional substrate of geotextile synthetic materialbetween the supporting substrate and the body of the dam.
 4. The methodaccording to claim 1, further comprising the step of disposing thewaterproofing geomembrane in correspondence of an upstream face of thebody.
 5. The method according to claim 4, further comprising the step offorming a freely deformable and bendable portion along a bottom edge ofthe geomembrane and fastening the portion with anchoring devices to afoundation of the dam.
 6. The method according to claim 5, furthercomprising the step of protecting the portion with a back-layer of fineloose material.
 7. The method according to claim 5, further comprisingthe step of providing a substrate of geotextile synthetic material toprotect the waterproofing geomembrane with respect to a layer ofballasting material resting on the portion.
 8. The method according toclaim 4 in which the waterproofing geomembrane comprises a plurality ofbands of sheet material, the method further comprising the step ofconstructing the waterproofing geomembrane by positioning the bandsside-by-side and downwardly extending in a direction of a slope of anupstream face of the dam.
 9. The method according to claim 4 in whichthe waterproofing geomembrane comprises a plurality of bands of sheetmaterial, the method further comprising the step of constructing thewaterproofing geomembrane by arranging the bands side-by-side,horizontally extending on an upstream face and in a direction of thelongitudinal axis of the dam.
 10. The method according to claim 9,wherein the waterproofing geomembrane is constructed starting from afoundation of the dam, to allow a partial exploitation of the dam duringits construction.
 11. The method according to claim 4, furthercomprising the step of welding pieces of synthetic material to repair adamaged part of the waterproofing geomembrane.
 12. The method accordingto claim 1, wherein the step of anchoring the waterproofing geomembraneis accomplished with L-shaped strips of synthetic material having aportion embedded into the transition zone and the body and including ananchoring wing welded to the waterproofing geomembrane against anupstream face of the dam.
 13. The method according to claim 12, furthercomprising the step of staggering the anchoring strips along horizontallines parallelly arranged to the longitudinal axis.
 14. The methodaccording to claim 12, wherein the anchoring strips are continuous, andfurther comprising the step of providing the continuous anchoring stripsalong horizontal lines, parallel to the longitudinal axis, for a part orwhole length of the dam.
 15. The method according to claim 1, whereinthe step of anchoring the waterproofing geomembrane is accomplished withC-shaped strips of synthetic material having end portions embedded intothe transition zone and the body and including an intermediate anchoringportion welded to the waterproofing geomembrane against an upstream faceof the dam.
 16. The method according to claim 1, wherein the transitionzone has a permeability and injectability between 1×10⁻¹ and 1×10⁻⁵cm/sec.
 17. The method according to claim 1, wherein the waterproofinggeomembrane is embedded into a core of fine loose material inside thebody.
 18. The method according to claim 1, further comprising the stepof forming the geomembrane in a central position of the body bydisposing two of the waterproofing geomembranes parallel and spacedapart in respect to the longitudinal axis, and providing a core of fineloose material in an intermediate zone between the two geomembranes. 19.A dam for impoundment of water, comprising: an embankment body ofsuperimposed layers of earth and/or rocks; a waterproofing barriercomprising plural waterproofing bands of geomembrane material arrangedside-by-side and having sealingly welded edges; a transition zone on atleast one side of the barrier and comprising superimposed layers ofloose material having a water permeability between 1×10⁻¹ and 1×10⁻⁵cm/sec; and said barrier further comprising anchoring strips that areheat-welded to said geomembrane material and at least partially embeddedin at least one of said transition zone and said body.
 20. The damaccording to claim 19, further comprising at least one protection layerof flexible synthetic material between each side of the waterproofingbarrier and the transition zone.
 21. The dam according to claim 19,wherein the geomembrane material comprises a layer of thermoplasticsheet material coupled to a supporting substrate of geotextile on atleast one side thereof.
 22. The dam according to claim 19, wherein thewaterproofing barrier is watertight fastened to an anchoring beamprovided parallel to a longitudinal axis of the dam and along a bottomperimeter of the body.
 23. The dam according to claim 22, wherein theanchoring beam is parallelly arranged to an upstream toe of the body andwherein the waterproofing barrier extends under the body towards theanchoring beam.
 24. The dam according to claim 19, further comprising adraining and monitoring pipe for water seeping through the waterproofingbarrier.
 25. The dam according to claim 19 having a rigid sidestructure, wherein the waterproofing barrier is watertight connected tothe rigid structure by at least one freely deformable waterproofingstrip.
 26. The dam according to claim 25, wherein the waterproofingstrip is shaped to form a set of bellows.
 27. The dam according to claim19, wherein the waterproofing barrier comprises first and second ones ofthe geomembrane material laterally spaced one from the other, and thetransition zone comprises a central transition zone of fine loosematerial between the two geomembranes, and side transition zones of fineloose material on each side of the geomembranes which are opposite tothe central transition zone.
 28. The dam according to claim 27, whereinthe two geomembranes extend parallel to a longitudinal axis of the dam.29. The dam according to claim 28, wherein the geomembranes compriseplural longitudinal strips which are alternatively inclined in oppositedirections on each side of the transition zone.
 30. The dam according toclaim 28, wherein the central transition zone between the twogeomembranes is connected to a drainage and monitoring pipe for waterseeping through the loose selected material of the central transitionzone.
 31. The dam according to claim 28, further comprising at least onetransverse partition of waterproofing material between the twogeomembranes.
 32. The dam according to claim 28, wherein the loosematerial of the central transition zone between the two geomembranes hasan injectability and waterproofing degree different from that of theloose material of the two side transition zones.
 33. The dam accordingto claim 19, wherein the loose material of the transition zone isgrouted with sealing substances in water seepage areas.
 34. The damaccording to claim 19, further comprising injection pipes forwaterproofing substances.
 35. The dam according to claim 19, wherein theanchoring strips are positioned along parallel rows on an upstream faceof the body.
 36. The dam according to claim 35, wherein the anchoringstrips of each of the rows are staggered in respect to the anchoringstrips of a contiguous one of the rows.
 37. The dam according to claim19, wherein at least a protection substrate of synthetic material isdisposed between the waterproofing barrier and the transition zone. 38.The dam according to claim 19, wherein the waterproofing bands areparallel to a slope of an upstream face of the dam.
 39. The damaccording to claim 19, wherein the waterproofing bands are parallel to alongitudinal axis of the dam from a bottom of the dam.
 40. The damaccording to claim 19, wherein the geomembrane material is folded tocreate a freely extensible portion along its lower edge.
 41. The damaccording to claim 40, further comprising a loose ballasting materialover the extensible portion of the geomembrane material.
 42. The damaccording to claim 41, further comprising a protection layer ofsynthetic material between the ballasting material and the extensibleportion of the geomembrane material.
 43. The dam according to claim 42,further comprising a layer of anti-grip material between the ballastingmaterial and the protection layer.
 44. The dam according to claim 19,wherein a lower edge of the geomembrane material is watertight andmechanically fastened to a base plinth along a bottom perimeter of thebody.
 45. The dam according to claim 19, wherein a lower edge of thegeomembrane material is fastened by watertight insertion to a baseplinth along a bottom perimeter of the body.